Personal History:

Research Interests:

Our studies are centered on the host factors that limit HIV infection. This interest started with our participation in a research effort that culminated in the discovery of CCR5 ligands RANTES, MIP-1α and MIP-1ß as potent natural inhibitors of HIV infection. The subsequent characterization by others of CCR5 and CXCR4 as co-receptors for HIV infection, and of the genetic defects of CCR5 that are associated with protection from infection reinforced our hypothesis that CCR5 ligands could participate in protection from infection. We were among the first to report, in a seminal paper published in the Proceedings of the National Academy of Sciences, that high chemokine levels are associated with AIDS-free status in the MACS cohort, and that subjects who remain uninfected despite a high-risk for HIV infection express high levels of MIP-1α. This study has led to collaborations with several clinical investigators. In particular, a collaborative effort sponsored by a five-year R01 grant with Dr. L. Temoshok, of our Institute, has addressed the link between chemokine levels, clinical status, and behavioral traits in a HIV cohort.

In recent years we became interested in the antiviral activities of the family of structurally related antimicrobial peptides known as defensins. In particular we chose to study beta defensins, because they are produced at high levels by epithelial cells in skin and mucosa, and may therefore be relevant to mucosal transmission of HIV. We reported that human beta-defensin (hBD) 2 and 3 inhibit replication of both X4 and R5 HIV. Since the antimicrobial activity of defensin is thought to be mediated mainly by disrupting the membrane of pathogens, we anticipated that HIV would be inhibited prior to entry. Unexpectedly, we found that hBD2 and 3 are active also after virus entry, and we hypothesized an intracellular mechanism of inhibition. Since CCR6 is a known cellular receptor for hBD2 and 3, we initiated studies on this receptor. We have now uncovered a fascinating mechanism of action. CCR6 ligands (hBD2, hBD3, and the chemokine MIP-3α/CCL20) trigger a post-entry activity which inhibits the accumulation of early reverse transcription products in HIV-infected cells.

Our data show that the main component of the inhibition is due to increased expression of the intracellular HIV restriction factor APOBEC3G. Interestingly, we observed increased APOBE3G levels in both resting and activated PBMC and purified CD4+ T cells. To our knowledge, this is the first time that induction of APOBEC3G has been observed in activated cells, i.e., cells that are a primary target of productive HIV infection. CCR6 is expressed on peripheral blood CD4+CCR5+ memory T cells, and by two populations of CD4+ T cells within the gut, α4β7+ and TH17, that have been implicated in cell-to-cell spread of HIV and enhanced restoration of CD4+ T cells within gut associated lymphoid tissue (GALT), respectively. The depletion of GALT CD4+ T cells is required but not sufficient to induce acquired immune deficiency syndrome (AIDS). This suggests that the loss of specific CD4+ T cell populations is a key step leading to disease progression and that protection of these populations is desirable for disease control. CCR6 is also expressed on activated macrophages and microglial cells. CCR6+ T cells are among the subsets most susceptible to HIV infection and their numbers are significantly decreased in HIV infected subjects, so that a protective mechanism based on CCR6 will likely have an impact on both therapeutic and preventive approaches to HIV infection.

This study has four aims 1) Identify APOBEC3G as the effector molecule of the antiviral activity mediated by CCR6 in primary cells. 2) Demonstrate that CCR6-induced signal transduction increases APOBEC3G expression and identify what is the critical specific pathway. 3) Demonstrate the efficacy of CCR6-mediated HIV inhibition on a broad spectrum of primary and non-B viral isolates. 4) Correlate the expression of CCR6, CCR6 ligands, and APOBEC3G with clinical status. We anticipate initiating more studies based on these findings, focused on boosting immunity to HIV in vaccines and microbicides.

We are developing a second line of studies on defensins. We have published our observation that hBD2 expression is not detectable by immunohistochemistry in the oral mucosa of HIV infected subjects, while robust expression is found in seronegative subjects. Since HIV does not infect epithelial cells that produce defensins, we hypothesized an indirect mechanism. Since the HIV-positive subjects that we investigated were undergoing antiretroviral therapy (ART), we tested whether ART agents modulated hBD2 expression. Our preliminary findings show that at least one ART agent inhibits hBD2 expression in cultured oral keratinocytes. We intend to further pursue these studies and apply for funding to study how decreased oral immunity might predispose HIV infected individuals to oral complication of AIDS. In particular, we are interested in the increased occurrence of HPV-associated lesions in the oral mucosa of HIV-infected subjects undergoing HAART. This increase is not due to differences in HPV strain prevalences and is therefore likely related to decreased immunity in the host.

In a new direction to our studies, we are collaborating with investigators within and outside the IHV to investigate whether certain types of cancers are related to known or novel human retroviruses. We will initially analyze clinical samples using PCR with primers targeted to known cancer-associated viruses and with degenerate primers targeting relatively conserved retroviral sequences. This study is in its developmental stages, and has received seed funding from the University of Maryland Cancer Center.